On March 13th, 2018 a group of 56 scientists, including many prominent researchers studying the effects of neonicotinoids, sent a letter to California’s Department of Pesticide Regulation (CDPR) highlighting the threat neonicotinoids pose to the health of California’s waterways.

The letter was prompted by findings from a 2016 Xerces Society investigation that were published in a report and subsequent fact sheet. That study found that imidacloprid is often found in California’s rivers and streams at levels harmful to species such as mayflies and caddisflies. Reducing the abundance of these insects has far-reaching effects because aquatic invertebrates are core contributors to nutrient cycling, water quality, and aquatic food webs that support fish and wildlife. The letter outlines some of the ramifications of such a change:

● Upsurges in pest species such as mosquitoes in the absence of predators and competitors;

● Increased methane production when microbes re¬place invertebrate decomposers; and

● Declines in native insectivorous birds and fish when food sources are limited.

The letter also points out that neonicotinoid contamination in California often exceeds federal aquatic life benchmarks. Between 2010 and 2015, 42% of California’s imidacloprid detections exceeded the acute benchmark and 100% of them exceeded the chronic benchmark. In certain regions of the state, particularly agricultural areas, the acute imidacloprid benchmark was more frequently exceeded. For example, the samples were above the acute benchmark in 80% of detections in the farmlands that straddle the San Luis Obispo and Santa Barbara county line near Santa Maria, and in 63% of detections in Monterey County. While the federal benchmarks don’t carry regulatory weight, exceedances often precede protective action.

The scientists urge CDPR to take steps to reduce neonicotinoid contamination of the state’s streams and rivers.